compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

cc/trees/proxy.h

Index: cc/trees/proxy.h
diff --git a/cc/trees/proxy.h b/cc/trees/proxy.h
index a8f3e99ca5670ea517ec01e2619275ec1dadc5e0..09592bc2cfac2684a759c2716a11b7ba08b12758 100644
--- a/cc/trees/proxy.h
+++ b/cc/trees/proxy.h
@@ -26,6 +26,7 @@ class Vector2d;
 namespace cc {
 class BeginFrameSource;
 class LayerTreeDebugState;
+class LayerTreeMutator;
 class OutputSurface;
 struct RendererCapabilities;
 
@@ -72,6 +73,8 @@ class CC_EXPORT Proxy {
       std::unique_ptr<BeginFrameSource> external_begin_frame_source) = 0;
   virtual void Stop() = 0;   // Must be called before deleting the proxy.
 
+  virtual void SetMutator(std::unique_ptr<LayerTreeMutator> mutator) = 0;
+
   virtual bool SupportsImplScrolling() const = 0;
 
   virtual void UpdateTopControlsState(TopControlsState constraints,